N-oxides of imidazo[4,5-b]quinoxalines and imidazo[4,5-b]pyrazines

The N-oxides and N,N-dioxides of methyl derivatives of imidazo[4,5-b]quinoxaline and imidazo[4,5-b]pyrazine were synthesized. The higher reactivity of the 2-methyl group in the N-oxides of 2-methylimidazo[4,5-b]quinoxaline as compared with the corresponding unoxidized derivatives was demonstrated.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1266–1270, September, 1972.     

Alkyl and 2-hydroxy derivatives of imidazo]4,5-b]pyrazine and their N-oxides

N-Monoxides and N,N-dioxides of some alkyl and hydroxy derivatives of imidazo[4,5-b]pyrazine were synthesized. It was proved that the nitrogen atoms of the pyrazine ring are oxidized; alkylation of N₁ sterically hinders oxidation of N₇. The hydrolytic cleavage of imidazo[4,5-b]pyrazines and their N-oxides was studied.     

Tautomerism of some imidazo[4,5-b]pyridine derivatives

It was shown by means of UV and IR spectroscopy and the ionization constants that the tautomeric equilibrium of 2-amino- and 2-mercapto derivatives of 3-methyl-3H-imidazo[4,5-b]pyridine is shifted to favor the amino and thione forms, respectively.     

Synthesis and antituberculotic activity of some new imidazo[4,5-b]pyridine derivatives

The reactions of 2-acetylimidazo[4,5-b]pyridine hydrazone with some alkyl-and arylisothiocyanates and some orthoesters were carried out. Various new derivatives of the titled compound such as thiosemicarbazones, ethoxymethylenehydrazones, and derivatives of the new pyrido-[3′,2′:4,5]imidazo[1,2-d][1,2,4]triazine ring system were obtained. Biological data for selected compounds are presented. Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1571–1579, October, 2006.     

Synthesis of imidazo[4,5-b]- and [4,5-c]pyridines

2-Arylimidazo[4,5-b]- and [4,5-c]pyridines have been prepared by treatment of the appropriate 2,3- or 3,4-diaminopyridine with an aromatic carboxylic acid in the presence of polyphosphoric acid. Other derivatives have been prepared by similar cyclisation of diaminopyridines using triethyl orthoformate, urea, thiophosgene and thiourea and the properties of some N-oxides have been investigated. A number of the arylimidazopyridines have been screened for mutagenicity.     

Synthesis of some pyridazino[4,5-b]quinoxaline derivatives

Several derivatives of the little-studied pyridazino[4,5-b]quinoxaline heterocyclic system, the structural isomer of benzopteridine, were synthesized in order to study their biological activity. 6,7-Dimethylquinoxaline-2,3-dicarboxylic acid and a number of its derivatives were also obtained.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 274–278, February, 1972.     

Synthesis of imidazo[4,5-b]pyridines from aminoimidazolecarbaldehydes

4-Amino-1,2-dimethylimidazole-5-carbaldehyde (1) and 5-amino-1-methylimidazole-4-carbaldehydes 3 were prepared by reduction of the corresponding aminoimidazolecarbonitriles 2 and 4. Condensation of 1 and 3 with carbonitriles, ketones and polyfunctional carbonyl compounds bearing the-CH₂CO-moiety afforded to the imidazo[4,5-b]pyridine derivatives.     

Synthesis and PMR spectra of 2-hetaryl-substituted imidazo[4,5-b]-pyridines and imidazo[4,5-c]pyridines

A simple method for the synthesis of 2-hetarylimidazopyridines based on the oxidation with sulfur of a mixture of p-diaminopyridine and heterocyclic compounds that contain an active methyl group is proposed. The reaction of diamines with N-oxides of of - and -picolines and the intramolecular oxidative cyclization of 3-amino-4-(2-pyridylmethylamino)pyridine lead to the same result. The PMR spectra of the synthesized 2-pyridylimidazopyridines were studied.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 940–947, July, 1989.     

Synthesis of furazano[3,4-b]pyrazine derivatives

Various furazano [3, 4-b] pyrazine derivatives were synthesized by condensation of 3, 4-diaminofurazan with substituted phenylglyoxals, cyclic di- and triketones, and diethyl acetylenedicarboxylate.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 613–615, May, 1978.     

Synthesis of imidazo[4,5-b]pyridines and imidazo[4,5-b]pyrazines by palladium catalyzed amidation of 2-chloro-3-amino-heterocycles

A facile synthesis of imidazo[4,5-b]pyridines and -pyrazines is described using a Pd-catalyzed amide coupling reaction. This reaction provides quick access to products with substitution at N1 and C2. A model system relevant to the natural product pentosidine has been demonstrated, as well as the total synthesis of the mutagen 1-Me-5-PhIP.     

Quaternization centers of N-methyl derivatives of imidazo[4,5-b]pyridine

It is shown that quaternization of isomers of 1-methylimidazo[4,5-b]pyridine and 3-methyl-imidazo[4,5-b]pyridine proceeds at different reaction centers — at the nitrogen atom of the imidazole ring in the first case and at the nitrogen atom of the pyridine ring in the second case.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1686–1688, December, 1973.     

Synthesis of disubstituted imidazo[4,5-b]pyridin-2-ones

Regioselective palladium-catalyzed amination of 2-chloro-3-iodopyridine followed by a subsequent palladium-catalyzed amination leads to 2,3-diaminopyridines. Treatment with triphosgene affords highly functionalized unsymmetrical imidazo[4,5-b]pyridin-2-ones in just three synthetic steps. A two-step synthesis of pseudosymmetrically disubstituted imidazo[4,5-b]pyridin-2-ones, 1,4-disubstituted pyrido[2,3-b]pyrazinediones, and 1,3-disubstituted thiadiazolo[3,4-b]pyridin-2-ones is also described.     

Preparation of 2-aryl-substituted imidazo[4,5-b]pyridines and imidazo[4,5-c]pyridines

It is proposed that sulfur be used as the oxidizing agent in the synthesis of 2-arylimidazopyridines from o-diaminopyridines and aromatic (heteroaromatic) aldehydes. Benzyl alcohols and benzylpyridinium salts can be used in place of aldehydes. 2-Phenylimidazopyridines are also formed in the thermal oxidation with sulfur of o-diaminopyridines with a benzyl substituent attached to the ring or exocyclic nitrogen atoms.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 639–645, May, 1987.     

Electrochemical properties of pyrido[1′,2′:1,2]imidazo[4,5-b]pyrazine and pyrido[1′,2′:1,2]imidazo[4,5-b]quinoxaline derivatives

The peak potentials (Ep) of 3-substituted pyrido[1′,2′:1,2]imidazo[4,5-b]pyrazine and pyrido[1′,2′:1,2]-imidazo[4,5-b]quinoxaline derivatives are sufficiently correlated with Hammett substituent constant ～_m and with the PM3 calculated LUMO energy levels, and the linear relationship between electron potentials of 9-substituted pyridoimidazoquinoxalines and the LUMO energy levels is also found out.     

Synthesis of pyrimido[4,5-b] indole derivatives

Chemistry of Heterocyclic Compounds -     

Synthesis and study of the structure of some pyridazino[4,5-b]quinoxaline derivatives

The structures of 1-oxo-4-hydroxypyridazino[4,5-b]quinoxaline and some of its methyl derivatives were established by IR and UV spectroscopy.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 556–561, April, 1973.     

Synthesis of aromatic pyrazolo[4,5-b]pyridine derivatives

Cyclocondensation of chalcones with 5-amino-3-methyl-1-phenylpyrazole leads to the formation of 2,4-diaryl-5-methyl-7-phenyl-3,4-dihydropyrazolo-[4,5-b]pyridines, which undergo aromatization upon treatment with N-bromosuccinimide.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1247–1251, September, 1987.